1. Field of the Invention
The present invention relates to a preparation of trans-polybutadiene using a novel bimetallic cobalt-aluminum adduct catalyst. More particularly, the present invention relates to preparing high trans-1,4-polybutadiene in the presence of a bimetallic cobalt-aluminum adduct catalyst having a stable oxidation state, which makes it possible to control the molecular weight of the polybutadiene and prevent the formation of gel and an oligomer so that the polybutadiene is odorless. The catalyst system comprising the bimetallic cobalt-aluminum metal adduct having a stable oxidation state makes it possible to prepare high trans-1,4-polybutadiene at high yield, can prevent an oligomer from being produced during polymerization, and thus can improve the physical properties of the trans-polybutadiene and prevent an odor from being caused by the oligomer. In addition, the reactivity of the catalyst can be controlled using novel activation systems comprising various allyloxy aluminum compounds.
2. Description of the Prior Art
Technology of preparing 1,4-trans-polybutadiene using butadiene as a monomer was reported long ago (Rubber Plast. Age 1963, 44, 42). In this technology, 1,4-trans-polybutadiene was prepared by polymerizing butadiene using a Ziegler-Natta catalyst system composed of a vanadium compound and alkyl aluminum. The prepared has a melting point (Tm) of 70˜130° C. higher than room temperature, and thus has a shortcoming in that it is required to be aged at high temperatures before blending with rubber. Various methods of preparing 1,4-trans-polybutadiene using catalyst systems other than the vanadium catalyst system have been reported.
Japanese Patent Application No. 67187 (1967) discloses preparing a polybutadiene having a trans content of 75-80% using a catalyst combination composed of a covalent compound, organoaluminum compound and a phenol compound.
U.S. Pat. No. 5,089,574 discloses a method of preparing 1,4-trans-polybutadiene by polymerizing 1,3-butadiene using a catalyst system composed of cobalt carboxylate, alkyl phenol, dialkyl sulfioxide and organoaluminum. In this method, the molecular weight of 1,4-trans-polybutadiene is controlled using CS2 in the catalyst system.
U.S. Pat. No. 5,448,002 discloses a method of preparing 1,4-trans-polybutadiene by polymerizing 1,3-butadiene using a catalyst system composed of cobalt carboxylate, alkyl phenol, dialkyl sulfoxide and organoaluminum. In this method, the molecular weight of 1,4-trans-polybutadiene is controlled using dialkyl sulfoxide in the catalyst system.
U.S. Pat. Nos. 6,310,152 and 6,617,406 disclose a method of preparing 1,4-trans-polybutadiene by polymerizing 1,3-butadiene in the presence of a catalyst system composed of cobalt carboxylate, para-alkylphenol or a para-alkylphenol/ortho-alkylphenol, and organoaluminum.
U.S. Pat. No. 5,834,573 discloses a method of preparing 1,4-trans-polybutadiene by polymerizing 1,3-butadiene in the presence of a catalyst system composed of cobalt acetylacetonate having an oxidation state of +3, alkylphenol, and organoaluminum.
U.S. Pat. No. 6,617,460 (2003) discloses a method of preparing 1,4-trans-polybutadiene using a Co(Oct)2 catalyst activated by Et3Al treated with p-dodecylphenol and o-phenylphenol. The resulting polymer consists of 70-85% 1,4-trans-enchainment and 15-30% 1,2-vinyl enchainment and has a melting point (Tm) lower than room temperature. The polymer having this structure has various advantages in terms of physical terms, but an oligomer is produced as a byproduct and becomes an obstacle in commercial production of the polymer.
Meanwhile, U.S. Pat. Nos. 5,025,059 and 6,608,154 disclose preparing trans-polybutadiene using barium thymolate/trialkylaluminum/alkyllithium.
Meanwhile, the application of 1,4-trans-polybutadiene to tires is disclosed in U.S. Pat. No. 5,025,059 (1991), U.S. Pat. No. 5,626,697 (1997), U.S. Pat. No. 5,753,761 (1998), U.S. Pat. Nos. 6,581,659 and 6,765,063, etc.
Problems in the production of trans-polybutadiene using conventional catalysts are that the molecular weight of trans-polybutadiene is high and not easy to control, and thus the Mooney viscosity of its compound is too high to be processed during rubber processing, and that the conversion of a monomer into the resulting trans-polybutadiene is low.